The present invention relates to 3D-shape measurement apparatuses and, more particularly, to a 3D-shape measurement apparatus which can suppress a reduction in measurement accuracy due to deformation of a scanning optical system, and variations in height accuracy depending on scanning positions, when the apparatus measures the 3D-shape of an object by linearly scanning the object with a laser beam or the like, employing a polarization/scanning/convergence means such as a polygon mirror and a fxcex8 lens, and then measuring the reflected light of the scanning light on the basis of the principle of triangulation.
Conventional methods for geometric-optically measuring a 3D-shape are roughly classified into two methods as follows: a method of projecting various kinds of lights to an object, and measuring the reflected lights with a photodetector, and a method of measuring an object with cameras from multiple directions under natural light or normal lighting, and obtaining the 3D-shape of the object according to the correlation between plural images.
The former method is further classified into various methods according to the method of light projection, the type of the photodetector, and the positional relationship between a light source and the photodetector.
FIG. 14 is a schematic diagram illustrating a conventional 3D-shape measurement apparatus which is widely used for industrial equipment.
With reference to FIG. 14, a light beam emitted from a light source 1 is polarized with a rotating mirror 2 such as a polygon mirror, and a scanning light beam 4 is converged by a convergence/scanning lens 3 such as a fxcex8 lens to form a spot light 6a on a target 5 to be measured. With rotation of the rotating mirror 2, the spot light 6a scans the target 5 along a straight line (hereinafter referred to as a scanning line 7) up to a spot 6b. 
Among light beams irregularly reflected at the surface of the target 5, a reflected beam 8 traveling in the direction different from the direction of the scanning beam 4 is focused to form an image on a position detector 10 such as a PSD or CCD camera through a photoreceptive optical system 9, and height data of a point irradiated with the spot light 6 is obtained by triangulation from position data of the image, which is obtained by converting the reflected light 8 into an electric signal.
The spot light 6 scans the target 5 along the scanning line 7, and the target 5 moves in synchronization with rotation of the rotating mirror 2, in the direction (sub scanning direction 12) perpendicular to a plane which is formed by the direction of the scanning line 7 (main scanning direction 11) and the direction 40 along which the scanning light 4 travels, whereby the spot light 6 scans the target 5 two-dimensionally, and the stereoscopic 3D shape of the target 5 is measured by storing and arranging the height data at the respective scanning positions on a memory.
FIGS. 15(a)-15(c) are diagrams for explaining problems of the height measurement by triangulation, in the conventional 3D-shape measurement apparatus.
Since, in the height measurement by triangulation, the reflected light is measured from the direction different from the direction of the scanning light 4, it is affected by the shape of the target 5 or the distribution of reflectivity. Accordingly, a blind spot occurs as shown in FIG. 15(a), or a height measurement error due to multiple reflection occurs as shown in FIG. 15(b).
FIG. 15(c) shows the case where the reflected light is measured from plural directions.
In FIG. 15(c), when the shape of the target 5 is complicated or the luminance change is considerable, reflected light beams 8a (a blind spot occurs), 8b (double-reflection occurs), 8c (no influence by the target 5), . . . are measured, and a height output value obtained from the reflected light beam 8c which is measured in the direction where no blind spot and no multiple reflection occur, must be selected.
FIG. 16 is a cross-sectional view illustrating the relationship between the scanning position and the image position of received light in the conventional 3D-shape measurement apparatus, for explaining the problems of triangulation in the case where the spot light 6 scans on the scanning line 7.
With reference to FIG. 16, in the conventional 3D-shape measurement apparatus, when the reflected light 8 from the target 5 is guided to the position detector 10 through a photoreceptive optical system 9 which is independent of the scanning optical system comprising the rotating mirror 2 and the convergence/scanning lens 3, the image position on the position detector 10 moves according to the scanning position, resulting in a height change H. Therefore, a position detector wider than the height measurement range is required, leading to degradation in performance, such as a reduction in measurement accuracy or a reduction in processing speed.
FIG. 17 is a perspective view illustrating the structure of the conventional 3D-shape measurement apparatus wherein the scanning optical system is included in the photoreceptive optical system.
With reference to FIG. 17, the photoreceptive optical system 9 shown in FIG. 14 is divided into a photoreceptive optical system 9a and a photoreceptive optical system 9b, and the scanning optical system is placed between the photoreceptive optical system 9a and the photoreceptive optical system 9b. 
The reflected light 8 reaches the position detector 10 through the scanning optical system, and a movement of the reflected light 8 according to the scanning position is canceled by the scanning optical system. Then, a movement of the image on the position detector 10 is mainly caused by a height change of the target 5, whereby the height measurement accuracy is increased, resulting in improved performance.
Furthermore, there is a 3D-shape measurement apparatus which solves the problems of triangulation shown in FIG. 15(c) by providing plural sets of the photoreceptive optical system 9a, the photoreceptive optical system 9b, and the position detector 10 shown in FIG. 17, and measuring the reflected light 8 from the target 5 from multiple directions.
The conventional 3D-shape measurement apparatuses are constructed as described above.
FIGS. 18(a) and 18(b) are diagrams for explaining a positional deviation of spot light, and a height error.
In the case where the conventional 3D-shape measurement apparatus measures the reflected light from multiple directions by straight-line scanning employing the scanning optical system to perform 3D-shape measurement by triangulation, when the photoreceptive optical system 9 which measures the reflected light 8 does not change and only the position of the spot light 6 on the target 5 changes from point A to point B as shown in FIG. 18(a), the image position on the position detector 10 changes from Axe2x80x2 to Bxe2x80x2, whereby the height of the target 5 cannot be measured accurately.
Especially when the spot light 6 is guided to the target 5 through the scanning optical system which comprises the polarization means by the rotating mirror such as a polygon mirror or a galvano mirror, and the convergence/scanning lens such as a fxcex8 lens, deterioration of the rotating part of the rotating mirror or deformation of the fxcex8 lens holder causes a deviation in the angle or position of the optical axis of the scanning light 4 with a change in environment such as temperature or with the passage of time, whereby the position of the spot light 6 changes, resulting in a difficulty in performing accurate height measurement.
Furthermore, in the case where the reflected light 8 is measured from multiple directions to accurately measure the height of the target 5 having a complicated shape as shown in FIG. 15(c), when the position of the spot light 6 changes from point A to point B as shown in FIG. 18(b), the image position on the position detector 10R changes from Axe2x80x2 to Bxe2x80x2 when the reflected light is received by the photoreceptive optical system 9R and the position detector 10R, and the target 5 is apparently positioned at a height of point Cxe2x80x2, resulting in an error hxe2x80x2 of the measured height.
On the other hand, when the reflected light is received by the photoreceptive optical system 9L and the position detector 10L, the image changes from Axe2x80x3 to Bxe2x80x3, and the target 5 is apparently positioned at point Cxe2x80x3, resulting in an error hxe2x80x3 of the measured height, which error is opposite to the height error hxe2x80x2 in regard to positive/negative and is different in size from the height error hxe2x80x2.
Since the direction and degree of the height error due to a positional deviation of the spot light 6 differ according to the direction of the reflected light, the error might be increased when selecting an accurate height of the target 5 from plural height data, leading to a fear that the height measurement accuracy is degraded.
As described above, when the height measurement by triangulation is carried out, a change in the position or angle of the spot light 6 must be suppressed to achieve highly accurate measurement. Therefore, in the case where scanning is carried out with the spot light 6 using the scanning optical system as described above, various restrictions are imposed on the height measurement as follows. A special scanning optical system for suppressing the influence of the angle change of the rotating mirror must be constituted, or deformation of the scanning optical system must be suppressed by restricting the usage environment, or periodical maintenance for correcting the height error must be carried out.
Further, the conventional 3D-shape measurement apparatus shown in FIG. 17 in which, in order to suppress a movement of the image according to the scanning position, the photoreceptive optical system 9 is divided into the photoreceptive optical system 9a and the photoreceptive optical system 9b, and the scanning optical system is placed between the photoreceptive optical systems 9a and 9b, and the reflected light 8 is guided to the position detector 10 through the scanning optical system, has the following problems.
FIG. 19 is a diagram illustrating a change in accuracy of height measurement according to the scanning position, in the conventional 3D-shape measurement apparatus.
With reference to FIG. 19, when the reflected light 8 of the spot light 6 is guided through the photoreceptive optical system 9a to the scanning optical system comprising the rotating mirror 2 and the convergence/scanning lens 3, the reflected light 8 curves in the path to the scanning optical system and travels an excess distance, or the spreading angle of the reflected light 8 changes in the photoreceptive optical system 9a, whereby the apparent light-emission point 13 of the reflected light 8 incident on the scanning/convergence lens 3 is not positioned on the scanning plane 16 on which the spot light 6 passing through the scanning/convergence lens 3 is focused.
In the case of a general scanning optical system, it is not guaranteed that a distance Ldr to the apparent focal point 14 of the reflected light 8 which has passed through the scanning optical system comprising the convergence lens 3 and the rotating mirror 2 is always constant regardless of the scanning position. At this time, a distance Lds to the apparent light-emission point 15 of the light which is emitted from the light source 1 to be inputted to the scanning convergence lens 3 is always constant regardless of the scanning position, whereby the position of the apparent focal point 14 varies while the position of the light-emission point 15 does not vary.
That is, since the focal point 14 of the reflected light 8 converged by the photoreceptive optical system 9b, and the distance to the photoreceptive surface of the position detector 10 vary according to the scanning position, the size of the image on the position detector 10 also varies. As the image size increases, the height measurement accuracy is degraded. Therefore, the height measurement accuracy also varies according to the scanning position.
As the result, even when the height measurement accuracy is maximized by minimizing the image size on the position detector 10 at a certain scanning position, the image size is large and a reduction in accuracy occurs at another scanning position, resulting in a reduction in the total height accuracy. Therefore, to maintain the height accuracy high, it is necessary to devise a scanning optical system considering a special photoreceptive performance, resulting in restrictions on design.
The present invention is made to solve the above-described problems and has for its object to provide a 3D-shape measurement apparatus whose accuracy of measurement is not reduced even when a scanning optical system comprising a rotating mirror and a scanning convergence lens deforms and the position of a spot light deviates, and a 3D-shape measurement apparatus which can suppress variations in height accuracy, without the necessity of employing a scanning optical system considering a special photoreceptive performance.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a 3D-shape measurement apparatus which detects a reflected light obtained by irradiating an object as a target of measurement with a scanning light beam by employing an optical position detector, and measures the 3D-shape of the object from the result of detection at each scanning position, and the apparatus comprises means for generating a light beam; polarization scanning means for polarizing the light beam to make the light beam perform scanning; scanning convergence means for converging the light beam which has passed through the polarization scanning means; and reflected light path changing means for guiding the reflected light from the target object located on a locus (hereinafter referred to as a scanning line) which is drawn by a focal point of the light beam (hereinafter referred to as a scanning light beam) which has passed through the scanning convergence means, toward the scanning convergence means and the polarization scanning means, to make the reflected light incident on the optical position detector, and changing, when the object moves in a direction perpendicular to both of the scanning light beam and the scanning line (hereinafter referred to as a sub scanning direction), the optical path of the reflected light so that the direction of a movement of the image obtained by the optical position detector in the sub scanning direction becomes the same as the direction of the movement of the object, and the moving distance of the image becomes less than twice as long as the moving distance of the object. Therefore, the position of the apparent focal point of the reflected light emitted from the scanning optical system, relative to the light source, becomes approximately constant regardless of deformation of the scanning optical system, whereby variations in the position of the image on the position detector are suppressed, and errors in measured heights are reduced.
According to a second aspect of the present invention, in the 3D-shape measurement apparatus according to the first aspect, the reflected light path changing means is constituted by an even number of, at least two, mirrors which are placed parallel to the scanning line. Therefore, errors in measured heights, which are caused by deformation of the scanning optical system, can be easily reduced by the combination of simple mirrors.
According to a third aspect of the present invention, in the 3D-shape measurement apparatus according to the second aspect, the relationship of relative positions between the mirrors is always kept constant. Therefore, even when the whole reflected light path changing means rotates about the axis of the main scanning direction, the positions of the apparent emission points of the reflected lights emitted from the reflected light path changing means become approximately the same, whereby errors in measured heights can be reduced.
According to a fourth aspect of the present invention, in the 3D-shape measurement apparatus according to the first aspect, the reflected light path changing means is constituted by a wedge-shaped prism having a light-incident surface and a light-outgoing surface which are parallel to the scanning line. Therefore, errors in measured heights, which are caused by deformation of the scanning optical system, can be easily reduced by the simple component. Furthermore, even when the whole reflected light path changing means rotates about the axis of the direction along which the scanning light travels, the positions of the apparent emission points of the reflected lights emitted from the reflected light path changing means become approximately the same, whereby variations in height data can be reduced.
According to a fifth aspect of the present invention, in the 3D-shape measurement apparatus according to the first aspect, the reflected light path changing means is constituted by a cylindrical lens which extends in the direction of the scanning line. Therefore, errors in measured heights, which are caused by deformation of the scanning optical system, can be easily reduced by the simple component. Furthermore, even when the whole reflected light path changing means rotates about the axis of the direction along which the scanning light travels, the positions of the apparent emission points of the reflected lights emitted from the reflected light path changing means become approximately the same, whereby variations in height data can be reduced.
According to a sixth aspect of the present invention, in the 3D-shape measurement apparatus according to the first aspect, the reflected light path changing means is constituted by a sheet-shaped optical element which refracts light. Therefore, errors in measured heights, which are caused by deformation of the scanning optical system, can be easily reduced by a single component. Furthermore, even when the whole reflected light path changing means rotates about the axis of the direction along which the scanning light travels, the positions of the apparent emission points of the reflected lights emitted from the reflected light path changing means become approximately the same, whereby variations in height data can be reduced. Moreover, restrictions on the placement of the reflected light path changing means are reduced, and the degree of freedom in design is increased, whereby more appropriate design is realized.
According to a seventh aspect of the present invention, in the 3D-shape measurement apparatus according to the third aspect, the even number of mirrors constituting the reflected light path changing means are formed at inner surfaces of a single prism body, and a correction prism for reducing an aberration of the image formed by focusing the reflected light on the optical position detector, is placed between the scanning convergence means and the optical position detector. Therefore, when the reflected light is diagonally incident on the light-incident surface or light-emission surface of the reflected light path changing means constituted by the prism, an aberration caused by the diagonal light incidence is corrected, whereby the size of the image on the position detector is reduced, and the accuracy of height measurement is improved.
According to an eighth aspect of the present invention, in the 3D-shape measurement apparatus according to the fourth or sixth aspect, a correction prism for reducing an aberration of the image formed by focusing the reflected light on the optical position detector, is placed between the scanning convergence means and the optical position detector. Therefore, when the reflected light is diagonally incident on the light-incident surface or light-emission surface of the reflected light path changing means constituted by the prism, an aberration caused by the diagonal light incidence is corrected, whereby the size of the image on the position detector is reduced, and the accuracy of height measurement is improved.
According to a ninth aspect of the present invention, in the 3D-shape measurement apparatus according to the fifth aspect, a cylindrical lens for reducing an aberration of the image formed by focusing the reflected light on the optical position detector, is placed between the scanning convergence means and the optical position detector. Therefore, when the reflected light is incident on the reflected light path changing means constituted by the cylindrical lens, an astigmatic aberration caused by the light incidence is corrected, whereby the size of the image on the position detector is reduced, and the accuracy of height measurement is improved.
According to a tenth aspect of the present invention, there is provided a 3D-shape measurement apparatus which detects a reflected light that is obtained by irradiating an object as a target of measurement with a scanning light beam by employing an optical position detector, and measures the 3D-shape of the object from the result of detection at each scanning position, and the apparatus comprises means for generating a light beam; polarization scanning means for polarizing the light beam to make the light beam perform scanning; scanning convergence means for converging the light beam which has passed through the polarization scanning means; and reflected light path changing means for guiding the reflected light from the target object located on a locus (hereinafter referred to as a scanning line) which is drawn by a focal point of the light beam (hereinafter referred to as a scanning light beam) which has passed through the scanning convergence means, toward the scanning convergence means and the polarization scanning means, to make the reflected light incident on the optical position detector, and changing the optical path of the reflected light so that an apparent emission point of the reflected light incident on the scanning convergence means is always positioned on a plane (hereinafter referred to as a virtual scanning plane) which passes through a locus drawn by an apparent focal point of the scanning light beam emitted from the scanning convergence means and is perpendicular to the scanning light beam. Therefore, the relative positions between the apparent focal point of the reflected light which is emitted from the scanning optical system and the apparent light-emission point of the light beam which is emitted from the light source become approximately constant regardless of the scanning position, whereby variations in the image size on the position detector according to the scanning position are reduced, and the accuracy of height measurement is improved.
According to an eleventh aspect of the present invention, the 3D-shape measurement apparatus according to the tenth aspect further includes converging distance changing means for changing the converging distance of the scanning light beam, which means is placed in an optical path along which the scanning light beam passing through the scanning convergence means reaches the scanning plane. Therefore, the position of the apparent scanning plane viewed from the scanning convergence means moves to the apparent emission point of the reflected light viewed from the scanning convergence means, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a twelfth aspect of the present invention, in the 3D-shape measurement apparatus according to an eleventh aspect, the converging distance changing means is constituted by at least three mirrors which are parallel to the scanning line. Therefore, when the apparent emission point of the reflected light is shifted in the scanning light traveling direction with respect to the scanning plane, the position of the apparent scanning plane viewed from the scanning convergence means can be moved in the scanning light traveling direction so as to match the position of the apparent scanning plane with the position of the apparent emission point of the reflected light, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a thirteenth aspect of the present invention, in the 3D-shape measurement apparatus according to the eleventh aspect, the converging distance changing means is constituted by parallel glasses having a light-incident surface and a light-emission surface which are parallel to the scanning line. Therefore, when the apparent emission point of the reflected light is shifted in the direction opposite to the scanning light traveling direction with respect to the scanning plane, the position of the apparent scanning plane viewed from the scanning convergence means can be moved in the direction opposite to the scanning light traveling direction with respect to the scanning plane so as to match the position of the apparent scanning plane with the position of the apparent emission point of the reflected light, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a fourteenth aspect of the present invention, the 3D-shape measurement apparatus according to the tenth aspect further includes reflected light emission point distance changing means for changing the distance up to an apparent emission point of the reflected light, which means is placed in an optical path along which the reflected light from the target object reaches the scanning convergence means. Therefore, the position of the apparent emission point of the reflected light viewed from the scanning convergence means can be moved to the scanning plane, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a fifteenth aspect of the present invention, in the 3D-shape measurement apparatus according to the fourteenth aspect, the reflected light emission point distance changing means is constituted by at least three mirrors which are parallel to the scanning line. Therefore, when the apparent emission point of the reflected light is shifted in the direction opposite to the scanning light traveling direction with respect to the scanning plane, the position of the apparent emission point can be moved in the scanning light traveling direction with respect to the scanning plane so as to match the position of the apparent emission point of the reflected light with the position of the apparent scanning plane, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a sixteenth aspect of the present invention, in the 3D-shape measurement apparatus according to the fourteenth aspect, the reflected light emission point distance changing means is constituted by parallel glasses having a light-incident surface and a light-emission surface which are parallel to the scanning line. Therefore, when the apparent emission point of the reflected light is shifted in the scanning light traveling direction with respect to the scanning plane, the position of the apparent light-emission point can be moved in the direction opposite to the scanning light traveling direction with respect to the scanning plane so as to match the apparent emission point of the reflected light with the position of the scanning plane, whereby stable height measurement can be always carried out regardless of the scanning position.
According to a seventeenth aspect of the present invention, in the 3D-shape measurement apparatus according to the fourteenth aspect, the reflected light emission point distance changing means is constituted by a cylindrical lens extending in the direction of the scanning line. Therefore, when the apparent emission point of the reflected light is not positioned on the scanning plane, the position of the apparent emission point is moved with respect to the scanning plane so that the apparent emission point of the reflected light is positioned on the scanning plane, whereby stable height measurement can be always carried out regardless of the scanning position.
According to an eighteenth aspect of the present invention, in the 3D-shape measurement apparatus according to the sixteenth aspect, the parallel glasses constituting the reflected light emission point distance changing means are provided with an even number of, at least two, mirrors at the inner surfaces, which mirrors are placed parallel to the scanning line, whereby the parallel glasses are integrated with each other. Therefore, the number of parts can be reduced by integrating plural means having different functions, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.
According to a nineteenth aspect of the present invention, in the 3D-shape measurement apparatus according to the eighteenth aspect, the integrated parallel glasses constituting the reflected light path changing means have a light-incident surface and a light-emission surface which are parallel to the scanning line and change the converging distance of the scanning light beam. Therefore, the number of parts can be reduced by integrating plural means having different functions, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.
According to a twentieth aspect of the present invention, in the 3D-shape measurement apparatus according to the fourth, sixth, or eighth aspect, the reflected light emission point distance changing means for changing the distance up to the apparent emission point of the reflected light is integrated with the prism constituting the reflected light path changing means. Therefore, the number of parts can be reduced by integrating plural means having different functions, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.
According to a twenty-first aspect of the present invention, in the 3D-shape measurement apparatus according to the twentieth aspect, the converging distance changing means, which comprises parallel glasses having a light-incident surface and a light-emission surface parallel to the scanning line and changes the converging distance of the scanning light beam, is integrated with the prism constituting the reflected light path changing means. Therefore, the number of parts can be reduced by integrating plural means having different functions, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.
According to a twenty-second aspect of the present invention, in the 3D-shape measurement apparatus according to the fifth aspect, the cylindrical lens constituting the reflected light path changing means is integrated with a reflected light emission point distance changing means which changes the distance up to an apparent emission point of the reflected light and is placed in an optical path along which the reflected light from the target object reaches the scanning convergence means. Therefore, the number of parts can be reduced, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.
According to a twenty-third aspect of the present invention, in the 3D-shape measurement apparatus according to the twenty-second aspect, the cylindrical lens constituting the reflected light path changing means is integrated with a converging distance changing means which changes the converging distance of the scanning light beam and comprises parallel glasses having a light-incident surface and a light-emission surface parallel to the scanning line. Therefore, the number of parts can be reduced, whereby the parts cost and the man-hours required for assembly and adjustment are reduced, resulting in a reduction in the total cost.